Protein catabolism and energy expenditure (EE) are increased in stress, trauma and sepsis. The hormones that have been shown to have the most dramatic effect upon metabolic rate and amino acid/protein metabolism are insulin, cortisol, and epinephrine. Epinephrine's most important metabolic effect is to increase EE, but epinephrine also dramatically causes the levels of most amino acids to fall. However, the effect of epinephrine upon amino acid kinetics is transient. Epinephrine has been suggested to reduce proteolysis, but we have not been able to demonstrate such an effect in humans. We have been able to demonstrate a transient increase in amino acid disposal. Possible mechanisms for this occurance are increased transport of amino acids into cells, increased amino acid oxidation, or increased protein synthesis. The results of our investigation of the effect of epinephrine upon amino acid and protein metabolism in humans suggests that protein synthesis may be effected by epinephrine. The ideal tracer for measuring protein synthesis in our hands contains two 13C atoms (i.e. [1,2-13C2]leucine) compared to the single 13C tracer we normally use, i.e. [1-13C]leucine. However, the whole body kinetics measured by the two tracers may be different with respect to oxidation because the 2nd carbon of leucine is released at a different biochemical step than the first carbon. For this reason we are measuring the oxidation and metabolism of the two leucine tracers. The results of this study should provide a method by which we and others using the 13C2-leucine tracer can compare their results of leucine kinetic measurements with results obtained using 13C1-leucine. This definition is required before we can apply the 13C2-leucine tracer to study how epinephrine may affect protein synthesis.